In order to isolate the occupants or other contents of a vehicle from road shocks and vibrations, that part of the vehicle weight which consists of the vehicle body, frame and engine plus transmission, is supported on the axles and wheels on springs having a low rate or force/deflection characteristic. Such comparatively soft springs are particularly necessary on vehicles with high pressure radial tires whose own isolation function is greatly reduced by their high effective spring rate.
However, the use of soft vehicle support springs gives rise to another problem, namely excessive body rollout due to the centrifugal force acting on the vehicle spring mass in sharp turns. In such turns, the comparatively high centripetal acceleration V.sup.2 /R of the sprung mass (vehicle velocity V, path radius R) requires large rollout spring deflections to make the sprung mass follow the path of the unsprung mass during the turn. Such large rollouts are undesirable because of passenger discomfort and because they can lead to loss of vehicle control.
The means used heretofore to reduce such vehicle rollout consist of either active powered systems or of passive restraints. In the active systems, pendulum-controlled hydraulic pumps deliver pressurized fluid to hydraulic actuators in a direction to oppose and counterbalance the overturning rollout moments. The hydraulic actuator reaction forces go directly to ground through the axles and wheels. In the system of passive restraints, comparatively stiff anti-roll torsion bars are used to bias either the front or rear pairs of wheels, or both. For example, a torsion bar extending from front wheel to front wheel is pivoted near its ends on the vehicle sprung mass (body or frame) on rubber grommeted bearings, and is joined to the axle and wheel assembly by a torque arm. This geometry retains the benefits of soft vehicle support springs for unsprung mass displacements when both wheels are displaced vertically the same amount. The torsion bar then simply rotates on its pivots, but has no twist torque. However, any tendency for vehicle roll, when one torque arm is displaced upwardly, while the other is displaced downwardly, results in torsion bar twist that resists the vehicle roll.
A disadvantage of the anti-roll torsion bar is that it nullifies the independent springing of all four wheels. For example, when the wheel at one end of the torsion bar is displaced by a pot-hole or raised obstacle, the resulting torsion bar twist transmits the wheel shock to the other corner of the vehicle. The torsion bar stiffness is thus added to the stiffness of the vehicle support springs and thereby increases the transmission of road shocks and vibrations to the vehicle body.
It is an object of my invention to eliminate vehicle rollout without the use of an active stabilizer system.
It is a further obJect of my invention to eliminate vehicle rollout completely without the use of a torsion anti-roll bar.
Still, another object of my invention is to provide truly independent springing at all four wheels with my passive anti-roll system and suspension geometry.